Peas belong to the family of legumes. These plants possess a unique capability due to their symbiotic relationship with bacteria called rhizobia. Peas are able to take nitrogen, an essential nutrient for plant growth, from the air and convert it into a form that plants can use, in a process called nitrogen fixation. These nitrogen-fixing bacteria reside in the root nodules of legumes. Once the legume plant dies, the fixed nitrogen is released into the soil, enriching it.

Potatoes (option 1), sorghum (option 2), and sunflowers (option 3) do not have the specific ability to fix nitrogen from the air and, therefore, contribute less to the nitrogen content of the soil. Sorghum and sunflowers are not legumes and lack the symbiotic relationship with the nitrogen-fixing bacteria. Meanwhile, potatoes, although they can improve the soil structure due to their deep roots, do not enrich the soil`s nitrogen content.